To grow properly, plants need nutrients (nitrogen, potassium, calcium, zinc, magnesium, iron, manganese, etc.) which normally can be found in the soil. Sometimes fertilizers are needed to achieve a desired plant growth as these can enhance the growth of plants.
This growth of plants is met in two ways, the traditional one being additives that provide nutrients. The second mode by which some fertilizers act is to enhance the effectiveness of the soil by modifying its water retention and aeration. Fertilizers typically provide, in varying proportions, three main macronutrients:
Nitrogen (N): leaf growth;
Phosphorus (P): Development of roots, flowers, seeds, fruit;
Potassium (K): Strong stem growth, movement of water in plants, promotion of flowering and fruiting;
three secondary macronutrients: calcium (Ca), magnesium (Mg), and sulphur (S);
micronutrients: copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn), boron (B), and of occasional significance there are silicon (Si), cobalt (Co), and vanadium (V) plus rare mineral catalysts.
The most reliable and effective way to make the availability of nutrients coincide with plant requirements is by controlling their release into the soil solution, using slow release or controlled release fertilizers.
Both slow release fertilizers (SRF) and controlled release fertilizers (CRF) supply nutrients gradually. Yet, slow release fertilizers and controlled release fertilizers differ in many ways: The technology they use, the release mechanism, longevity, release controlling factors and more.
Solid fertilizers include granules, prills, crystals and powders. A prilled fertilizer is a type of granular fertilizer that is nearly spherical made by solidifying free-falling droplets in air or a fluid medium. Most controlled-release fertilizers (CRFs) used in commercial nurseries are prilled fertilizers that have been coated with sulfur or a polymer. These products have been developed to allow a slow release of nutrients into the root zone throughout crop development.
Nutrients are released out of coated fertilizer prills through osmosis at a rate that is positively correlated with increased temperature. The release rates are associated with the type and/or thickness of the coating on the fertilizer prill granule.
CRF fertilizers are available with different longevities. Most manufacturers have products with 3, 6, 9, or 12-month release periods. Products with different longevities are manufactured by blending fertilizer prills of different coating thicknesses: the thinner coated prills release nutrients first and then the thicker-coated prills release nutrients later. Short-term crops such as annuals would probably require 3-month release products and longer-term crops such as woody perennials would require fertilizer products with a 12-month release period.
U.S. Pat. No. 2,935,387 teaches a compacting process for producing a granular product.
U.S. Pat. No. 3,026,194 discloses a method of improving muriate of potash particles previously compacted and dried from fines comprising wetting said particles with a useful amount of an aqueous solution, and drying the particles, whereby the physical competency of the particles is improved.
U.S. Pat. No. 3,048,478 relates to a method for producing a granular, chemical salt of superior storage qualities, and more particularly to a method which include a step of sintering a narrow size range of particles of a granular inorganic salt to produce densified particles which are less frangible and have better storage and handling qualities.
GB 1079673 teaches improvements in or relating to agglomeration of potash containing material, wherein finely divided granular potash containing salt ore, e.g. <48 mesh, is agglomerated, e.g. for fertilizer application, by wetting the fines with an aqueous solution containing hydrofluoric acid or a metal fluoride, forming the wetted particles into aggregates, e.g. in a pelletizing drum or on a pelletizing disc or balling drum, and hardening the aggregates by drying at an elevated temperature below the fusion temperature, e.g. 200° to 650° C. The hydrofluoric acid or metal fluoride solution may be applied prior to, during or subsequent to pelletizing and the preferred solution contains about 10 percent by weight of the fluoride compound which is used in a ratio by weight to the granular material of about 2:100. The pellets are preferably agitated during the drying process.
GB1073682 teaches a process for compacting muriate of potash, wherein a mixture of potassium chloride and up to 10 percent of an additive consisting of urea, ammonium nitrate or a mixture of ammonium nitrate and phosphate having a m.p. below 400° F. is compacted at a pressure of 200-10,000 pounds per linear inch per bearing by the use of a single or double roll compactor and the resulting sheet material is comminuted. The additive may be mixed dry or a concentrated solution or suspension. Compaction may be at 20-80° C.
U.S. Pat. No. 3,513,230 teaches a process for improving the resistance to physical breakdown of potassium sulfate compacts formed by compacting particulate potassium sulfate feed material under pressure. The resistance to physical breakdown of such compacts is improved by controlling the moisture content of the feed material during compaction to between about 0.5% and 2.0% by weight and compacting the feed material at a pressure within the range of between about 12,000 and 40,000 p.s.i. The resistance of such compacts to physical breakdown is further improved by compacting the feed material at a temperature of approximately 90° C. The potassium sulfate compacts may be subjected to granulation to provide a quantity of granules having improved resistance to physical breakdown. The resistance of such granules to physical breakdown may be further improved by moistening the granules with water and thereafter evaporating the Water from the moistened granules.
U.S. Pat. No. 3,532,486 relates to an improved method for compacting and subsequently granulating liquid hydrocarbon-containing water-soluble solid particle fines by admixing with such contaminated fines a small amount of liquid hydrocarbon free pure water-soluble fines of the same material and thereafter compacting and granulating the fine mixture.
CA988315 discusses compaction of potash
U.S. Pat. No. 6,379,414 teaches A process is for the production of potash fertilizer granulates which have a stable shelf life also at high relative air humidities. This granulate contains an additive in the form of magnesium oxide and/or calcium oxide in a fine powder form, which is added by metering in prior to the compacting step. The result is a high final bursting strength even if the granulate is stored in a wet climate.
US2010040882 discloses a method for forming a potassium chloride particle from potassium chloride powder having resistance to moisture absorption and shrinkage. The original feedstock comprises potassium chloride in a size distribution of 30 mesh and 100 mesh as well as a gluten based binder.
US 20130031943 discloses a granular cohered MOP fertilizer having one or more micronutrients, and one or more binding ingredients. The fertilizer is prepared by compacting MOP feed material with one or more micronutrients and one or more optional binders to form a cohered MOP composition. The cohered MOP composition is then further processed, such as by crushing and sizing, to form a cohered granular MOP product containing micronutrients.
It is preferable than no more than 20% of the particles of the powder will have a particle size of less than 150 μm (also referred to herein as “fertilizer dust” or “dust”) because having more than 20% of the particles of the powder with a particle size of less than 150 μm will cause the bulk density of the overall mass of the powder to be too low for an efficient process, causing, for example, to the shaking of the machine, the final product having increased porosity, high occurrence of process shutdown and the like.